1. Technical Field
This disclosure relates to marine electromagnetic (EM) surveys, and more particularly, to the control of an EM source used in a marine EM survey.
2. Description of the Related Art
Marine electromagnetic (EM) surveys are a relatively new technique used in energy exploration. In a marine EM survey, a sub-sea EM source may be towed in the water by a tow vessel. The sub-sea EM source may be towed at a depth that may vary with the portion of the sea or ocean in which the exploration is conducted. The EM source may transmit electrical current through the water between two electrodes, thereby producing an EM field. Distortions in the field may indicate the presence of valuable deposits, such as oil deposits, natural gas deposits, and so on. A response obtained during the conducting of an EM survey may be compared with various baselines to determine if any such distortions correspond to valuable deposits.
In addition to the sub-sea source, the tow vessel may include a significant amount of equipment used to generate the electrical energy for the resulting EM field. Equipment on a tow vessel may include a high power frequency converter coupled to the vessel's power source. The frequency converter may provide a regulated low-voltage alternating current (HVAC) output. The frequency converter may also be synchronized to a global positioning system (GPS) receiver, and thus its output may vary with a geographic location. A step-up transformer on the vessel may be used to increase the voltage (and thus, decrease the current). The output signal from the transformer may be transmitted via tow cable to the sub-sea EM source, wherein the voltage may be reduced by a step-down transformer, and the resulting current may be transmitted between two electrodes in order to produce the desired EM field.
While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and description thereto are not intended to be limiting to the particular form disclosed, but, on the contrary, is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.